The present invention relates to an electric rail vehicle provided with an electrical power supply unit.
It is common practice for such an electric vehicle, which may be a locomotive or a motor car or coach, to be powered via a catenary delivering an AC working voltage.
The invention relates more particularly to such a vehicle that is equipped with a load, such as a transformer, and with an electrical power supply unit for electrically powering said load from the catenary. The power supply unit conventionally includes electrical switchgear, such as a circuit-breaker, that protects the high-voltage AC circuits of the rail vehicle.
However, such a configuration suffers from certain drawbacks. Currents appear whose gradients as a function of time are very steep. By way of example, when the AC normal working voltage is 25 kV at 50 Hz, currents of 300 A are generated in about 5 ns. They give rise to interference that can damage, or, at the least, hinder proper operation of equipment situated in the vicinity-of the electrical switchgear, e.g. such as on-board control electronics.
In order to mitigate those drawbacks, an object of the invention is to provide an electric rail vehicle equipped with an electrical power supply unit that gives rise to low electromagnetic interference only, so as to guarantee that no damage is done to the structural integrity of the various items of electrical and electronic equipment with which the vehicle is provided.
To this end, the invention provides an electric rail vehicle, in particular an electric locomotive, designed to be powered via a catenary, said vehicle including a load, in particular a transformer, and an electrical power supply unit for powering said load from said catenary, via electrical switchgear, in particular a circuit-breaker, said vehicle being characterized in that said power supply unit includes an interference attenuator of the ferrite type for attenuating interference due to switching.
According to an advantageous characteristic of the invention, said interference attenuator is placed between said catenary and said electrical switchgear.
The interference attenuator of the ferrite type for attenuating interference due to switching is known, for example, from JP-A-1 086 425 and JP-A-4 322 024. In those documents, such an attenuator is constituted by a cylinder made of ferrite and disposed around an electrical line situated downstream from the electrical switchgear. The ferrite cylinder behaves as an inductor whose inductance increases with increasing current frequency.
Because of the presence of metal members disposed in the vicinity of the conductor connecting the catenary to the circuit-breaker, stray capacitance forms in the vicinity of the roof of the rail vehicle and upstream from the switchgear. A transmission line constituting an electromagnetic waveguide is created between said upstream stray capacitance and the switchgear proper.
On closing the switchgear, when a voltage is applied across the two electrodes of said switchgear, an electric arc strikes in it. Under certain circumstances, in particular when the switching of the electrical switchgear is based on vacuum xe2x80x9cbottlexe2x80x9d switching, said electric arc is extremely unstable, i.e. it is subjected to multiple interruptions followed by corresponding re-strikes. Such arc instability corresponds to successive breaks and re-makes that generate electromagnetic interference resulting in steep current gradients which can damage or hinder proper operation of equipment situated in the vicinity of the electrical switchgear.
Because of the frequency, current, and voltage to which the electric rail vehicle is subjected, the interference attenuator of the ferrite type for attenuating interference due to switching is used for its resistive portion, rather than for its inductive portion as in the above-mentioned Japanese patent applications. By providing such an interference attenuator, it is possible to reduce the steep current gradients DI/DT generated on circuit-breaker closure, in particular when the attenuator is placed upstream from the switchgear. Rather than modifying the current oscillations, this contributes to preventing them from forming by reducing the value DI/DT, which is what can generate such oscillations.
In the invention, instead of seeking to filter out a steep current gradient DI/DT initiated previously by the switchgear, the switchgear is forced to switch less rapidly, by influencing the physical establishing of the arc under a vacuum in the xe2x80x9cbottlexe2x80x9d.
The invention also provides an electrical power supply unit, in particular for an electric rail vehicle, for powering a load, in particular a transformer, from a power source via electrical switchgear, in particular a circuit-breaker, said power supply unit including an interference attenuator of the ferrite type for attenuating interference due to switching, said power supply unit being characterized in that said interference attenuator is placed between said power source and said electrical switchgear.